The digital platforms on the current market offer multi-services through wireless links. Therefore, they must be capable of supporting various standards, especially the standards implemented for wireless high bit rate communications such as the IEEE802.11a, b, g standards, and now the 802.11n standard for the WIFI function. This type of wireless communication also takes place inside closed premises where, in particular, very penalizing electromagnetic wave propagation conditions are observed. To improve the system loss and the bit rate between two wireless devices, a technique known as MIMO (for ‘Multiple Output Multiple Input’) is used. This technique requires at least two antennas, a good de-correlation as well as a good isolation between the antennas.
To respond to the problem of the isolation between two antennas, the solution typically used is to spatially distance the antennas from each other in order to ensure a sufficient isolation. However, this solution does not allow a compact system to be obtained.
Another solution allowing the isolation between two antennas to be improved has been presented in the article by A. DIALLO, C. LUXEY, Ph. LE THUC, R. STARAJ, G. KOSSIAVAS, entitled “Enhanced two-antenna structures for universal mobile telecommunications system diversity terminal”. IET Microwaves, Antennas and Propagation, vol. 2, no 1, p. 93-101, February 2008. This solution proposes to connect two PIFA type antennas, i.e. F-inverted antennas by means of a conductive line. This suspended conductive line is directly connected to the antenna at the antenna short circuit point and can compensate for the electromagnetic coupling existing between the two antennas. This line brings a fraction of the signal from an antenna to the other, which isolates them more or less according to the length of the line.
It has also been proposed to add quarter wave notches between two antennas to increase the isolation between antennas.